tests/rv_connect.py: Catch a more specific exception

Signed-off-by: NLucas Meneghel Rodrigues <lmr@redhat.com>

tests/rv_connect.py

@@ -147,7 +147,7 @@ def launch_rv(client_vm, guest_vm, params):
     # Launching the actual set of commands
     try:
         client_session.cmd("startx &", timeout=15)
-    except:
+    except ShellCmdError:
         logging.debug("Ignoring an Exception that Occurs from calling startx")
 
     wait_timeout(15)